1. Field of the Invention
The present invention relates to an optical pickup actuator recording or reproducing information onto an optical disc, and in particular to an optical pickup actuator which is capable of performing a tracking movement with a focusing and a tilt movements.
2. Description of the Conventional Art
Generally, an optical pickup apparatus includes an optical pickup actuator as an object lens focusing an optical spot of an optical beam at the center of a signal track of an optical disc by corresponding to a surface vibration and eccentricity of the optical disc in accordance with rotation of the optical disc.
The optical pickup actuator operates in order to make the object lens perform a focusing and a tracking movements.
Herein, the focusing movement is moving an object lens up and down in order to make an optical spot of an optical beam of the object lens place within a depth of focus on a signal track of an optical disc, and the tracking movement is moving the object lens right and left in order to make the optical spot of the optical beam of the optical lens follow the center of the signal track.
Accordingly, the optical pickup actuator follows the center of the signal track of the optical disc by moving the object lens up and down (focusing servo), right and left (tracking servo) according to a current flowing on a coil and an electromagnetic force between magnets.
FIGS. 1, 2, 3 schematically illustrate an optical pickup actuator in accordance with the conventional art.
As depicted in FIG. 1 illustrating the optical pickup actuator in accordance with the conventional art in the information recording aspect, the optical pickup actuator in accordance with the conventional art includes an object lens 2 focusing an optical beam from a laser diode light source at an information recording surface of an optical disc, a bobbin 4 supporting the object lens 2, two magnets 6 respectively placed at the front and the rear of the bobbin 4, a yoke 8 placed at the rear of the magnet 6 and preventing leakage of magnetic flux from the rear of the magnet 5, a tracking coil 10 placed at the exterior of the bobbin 4 so as to be corresponded to the magnet 6 and a focusing coil 12 wound around the bobbin 4 so as to be at right angles to the tracking coil 10
The optical pickup actuator in accordance with the conventional art performs the focusing movement and the tracking movement by having the tracking coil 10 and the focusing coil 12 within a magnetic space formed with the magnet 6 and the yoke 8 and moving the object lens 2 up-down and right-left by Lorentz force of Fleming""s left-hand law.
In more detail, as depicted in FIG. 2 illustrating the optical pickup actuator in accordance with the conventional art taken along the line Axe2x80x94A of FIG. 1, a magnetic circuit of the actuator for performing the focusing movement is constructed with the focusing coil 12, the magnet 6 magnetized to form a NS and the yoke 8 placed at the rear of the magnet 6.
Herein, a line of magnetic flux is generated in a horizontal axis direction, and the direction of power N operating the optical pickup actuator works in up and down directions, accordingly the focusing movement is performed.
In addition, as depicted in FIG. 3 illustrating the optical pickup actuator taken along the line Bxe2x80x94B of FIG. 1, the magnetic circuit of the optical pickup actuator for the tracking movement is constructed with the magnet 6 magnetized to form N, S polar and the tracking coil 10 placed horizontally at both sides of the magnet 6 on the boundary surface of the magnet 6.
Herein, the line of magnetic flux is generated in a direction vertical to the ground, and the power N operating the optical pickup actuator works in the right and left directions according to the direction of the current I applied to the tracking coil 10, accordingly the tracking movement can be performed.
And, as depicted in FIG. 1, the pickup actuator further includes a wire spring 14 and a PCB (printed circuit board) 48 mechanically connected to a fixed part (not shown) by having a fixation point at the right and left sides of the bobbin 4.
As described above, the optical pickup actuator in accordance with the conventional art operated by the magnetic force generated in the magnetic circuit and working in the up-down (focusing) and left-right (tracking) directions performs the focusing movement and the tracking movement by performing the up-down movement and the left-right movement on the basis of the front end portion of the wire spring 14 fixed to the fixed part.
According to the thinness trend of the optical pickup system, in the optical pickup actuator in accordance with the conventional art, it is difficult to form a magnetic circuit on a light path of the laser diode light source.
In the meantime, as described in FIG. 4 illustrating another optical pickup actuator in accordance with the conventional art, the magnetic circuit is constructed so as to avoid the light path of the light source.
In more detail, as depicted in FIG. 4, another optical pickup actuator in accordance with the conventional art includes an object lens 34 focusing a light beam from a light source on an information recording surface of an optical disc, a lens holder 35 supporting the object lens 34, magnets 38 placed inside the lens holder 36, yokes 40 placed at the rear of the magnets 38 and preventing leakage of magnetic flux from the rear of the magnets 38, a tracking coil 42 installed at the lens holder 36 so as to be corresponded to the magnets and a focusing coil 44 wound around the inside diameter of the lens holder 36 so as to be at right angles to the tracking coil 42.
And, another optical pickup actuator in accordance with the conventional art further includes a wire spring 46 and a PCB 48 (printed circuit board) placed at the right and left sides of the lens holder 36, supplying a current to the tracking coil 42 and the focusing coil 44 and supporting the lens holder 36.
Herein, the lens holder 36 has a protrusion portion 36b in which the object lens 34 is fixed in order to avoid a light path from the light source, and rectangular holes 36a, 36axe2x80x2 are formed at the lens holder 36 in order to place the magnets 38 and the yokes 40 at the center portion of the lens holder 36.
As depicted in FIG. 4, in another optical pickup actuator in accordance with the present invention, the up-down movement and the right-left movement of the lens holder 36 according to the tracking movement and the focusing movement are biaxial-operated on the basis of the end portion of the wire spring 46.
However, in the optical pickup actuator projecting the object lens 34, because the magnet 38, the yoke 40 and the tracking coil 42, etc. for the focusing and the tracking movements are inserted into the holes 36a, 36axe2x80x2 of the lens holder 36, a resonance point is lowered in high frequency characteristics. And, because the object lens 34 is installed at the protrusion portion 36b, the fixation point of the wire spring 46 becomes far off from the object lens 34, accordingly unstable movement can occur in a high speed mode.
In addition, in the optical pickup actuator in accordance with the conventional art projecting the object lens 34, because a separation distance of an excitation force center of the tracking and an excitation force center of the focusing divided into the upper and lower parts is relatively long, a resonance point is lowered and vibration characteristics in the surface direction are bad.
In the meantime, a higher accuracy is required for the optical pickup actuator and a tilt margin of the actuator is gradually lowered in the operation of the actuator, it is impossible to satisfy an optical tilt permissive error by the conventional assembly method.
Accordingly, in the recent optical pickup actuator, besides the focusing and tracking biaxial servo, a triaxial actuator following disturbance about a radial tilting and operable on three axes is required.
According to the thin trends of product such as a portable computer, because of limitation conditions as overlapping the light path and the actuator, in the conventional biaxial actuator forming a magnetic circuit is avoided as depicted in FIG. 1, and the object lens is projected so as to separate from the light path as depicted in FIG. 4, in the structure of FIG. 4, constructing a magnetic circuit for tilt operation is more difficult.
In the meantime, in the optical pickup actuator adapting a wire method performing a biaxial linear motion and a plate spring method in accordance with the conventional art, in order to decrease a height of the optical pickup, the light path from the laser diode light source has to be constructed on a same flat surface with the optical pickup actuator.
In this case, because a magnetic circuit such as a magnet, a focusing coil, a tracking coil, etc. for the focusing movement and the tracking movement exists on the light path from the laser diode, it is difficult to thin the actuator.
Accordingly, it is an object of the present invention to provide an optical pickup actuator which is capable of performing a radial tilt movement with a focusing and a tracking movements and thinning an optical pickup apparatus by placing a focusing/tilt operating magnetic circuit at the center portion and placing a tracking operating magnetic circuit at the right and the left portions.
In order to achieve the above-mentioned object, an optical pickup actuator in accordance with the present invention includes a lens holder having an object lens focusing an optical beam on an information recording surface of an optical disc and having a hole at the center portion, a focusing/tilt operating means placed inside the hole of the lens holder and generating a magnetic force so as to operate the lens holder in a focusing or a tilt direction and a tracking operating means respectively installed at the right and left sides of the lens holder and generating a magnetic force so as to operate the lens holder in the tracking direction.
The lens holder has a protrusion portion so as to be installed the object lens, and wire springs 60 are connected between the both sides of the protrusion portion 52a and supporting means.
In an embodiment of the present invention, the focusing/tilt operating means includes a first magnet fixed inside the hole of the lens holder and a focusing coil fixed to a pickup base, projected inside the hole of the lens holder and mutually operating with the first magnet.
In addition, the tracking operating means includes a second magnet respectively fixed to the right and the left sides of the lens holder and tracking coils installed at a yoke of the pickup base so as to correspond to the second magnet.
Herein, the first magnet and the second magnet are made of one of neodymium (Nd), sintered magnet and plastic magnet.
The first magnet is constructed as a pair, and the magnet faces each other inside the hole of the lens holder and is installed so as to be parallel with the track direction.
The focusing coil is constructed as a pair divided into the right and the left directions between the pair of first magnets, and each focusing coil has a rectangular ring shape.
The pair of focusing coil are parallel-connected each other and respectively and independently generate power in up and down directions according to applied power.
In addition, the pair of first magnets are magnetized to form a multipolar magnetization in the upper and lower directions and magnetized in the front and back, accordingly a line of magnetic flux in different directions is generated by the pair of focusing coils corresponded each other.
The pair of focusing coils divide and interlink a coil placed at the other polar and having magnetic flux in the same direction in order to be offset each other.
The second magnet is magnetized to form a unipolar magnetization, the tracking coil is formed so as to have a rectangular ring shape and has a size in which the second magnet is insertable.
In addition, in accordance with another embodiment of the present invention, the focusing/tilt operating means includes a first magnet fixed inside the hole of the lens holder, a focusing coil fixed to a pickup base, projected inside the hole of the lens holder and generating the operating force in the focusing direction by mutually working with the first magnet and tilt coils divided into right and left portions so as to be parallel with the focusing coil and generating the operating force in a radial tilt direction.
In addition, the tracking operating means includes second magnets respectively fixed to the right and the left sides of the lens holder and tracking coils installed at a yoke of the pickup base.
Herein, the first magnet, the focusing coil, and the tilt coils are arranged so as to be parallel each other, and the tilt coil is constructed as a pair and the current is applied in different directions.
The tracking coil has a rectangular ring shape and has a size in which the second magnet is insertable.
In addition, in yet another embodiment of the present invention, the focusing/tilt operating means includes focusing coils fixed inside the hole of the lens holder and a first magnet fixed to a pickup base, placed inside the lens holder and mutually working with the first magnet.
The tracking operating means includes tracking coils wound around the right and left sides of the lens holder and performing the tracking operation and second magnets fixed to the yoke placed at the right and the left sides of the lens holder so as to be corresponded to the tracking coils.
Herein, the focusing coil is constructed as a pair divided into the right and the left portions inside the hole of the lens holder.
The pair of focusing coils are connected so as to be parallel each other and generate respectively and independently the power in the up and down directions.